In cracking operations, such as in the pyrolytic cracking of ethane, propane, and naphtha to form olefins, oxygenated compounds including carbonyl compounds such as aldehydes and ketones are formed. The amount of carbonyl compounds formed in such operations can vary widely, but is typically about 1-100 ppm in the product gas stream. Concentrations as high as 1000 ppm are occasionally encountered depending upon the use of various feedstocks and cracking temperatures. The product gas stream is typically passed through a basic wash (pH&gt;7) to remove acidic components such as hydrogen sulfide and carbon dioxide. Oxygen containing compounds, particularly acetaldehyde, tend to undergo polymerization in the presence of the basic wash or scrubbing conditions.
In the caustic scrubbing system of such plants, the polymers of acetaldehyde and other oxygenated compounds are able to mix with the caustic, which may form an emulsion. In some plants this emulsion can become severe enough to be a bottleneck to plant operations. In other plants, the polymers are removed quite easily from the caustic scrubbing system along with the spent caustic. The spent caustic and polymers are then pumped to an accumulator or surge drum.
In the surge drum, hydrocarbon and aqueous layers are separated. The hydrocarbons are lighter than water and float to the top of the drum, where they are skimmed off and disposed of. Caustic which has separated from the hydrocarbon is then treated in various ways and returned to the caustic scrubbing system. Unfortunately, the acetaldehyde polymer and other organic polymers occasionally form stable emulsions in the surge drum, and these emulsions seriously interfere with the separation of caustic and hydrocarbons in the surge drum. The hydrocarbons then contain too much caustic to be disposed of, and less caustic is available to be restored to the system. At the present time there exists a continuing need for an effective demulsifier to break the troublesome emulsions into two distinct layers.